1. Field of the Invention
The present invention relates to a method of manufacturing thermoplastic resin molded optical members such as, for example, optical assembly members, preforms of plastic optical fibers, or light wave guides.
2. Description of the Related Art
Conventionally, according to the kinds of products to be molded, thermoplastic resin molded optical members such as optical assembly members, plastic optical fibers, or light wave guide members, are manufactured by executing either an extrusion molding process or an injection molding process. Nevertheless, all of these conventional methods of manufacturing such thermoplastic resin molded optical members still have a variety of technical problems to be solved.
When manufacturing molded optical members by using an extrusion molding process, normally, there are a number of grooves in the resin path of any extrusion molding machine to cause resin material to easily build up inside as a result of the movement of the screw of the molding machine. This in turn prevents resin material simultaneously delivered to the extrusion molding machine from a hopper from simultaneously being extruded. Part of the resin material adheres to the screw as a result of the occurrence of convection, resulting in depositing of resinous residue.
On the other hand, if a high temperature is used in the molding process, then the heated screw causes the adhered resin to be degraded to cause discoloration. The color-borne resin material is then blended with fresh resin material supplied to implement the following molding process, and is then extruded from the molding machine. As a result, the molded product bears an unwanted color.
On the other hand, when producing molded optical members using injection molding, distortion occurs internally in the molded pieces. Once the distortion internally occurs, it easily causes the molded piece to crack. Any molded product containing internal distortion is not suited for use as an optical member. Furthermore, the injection molding process is not suited for the production of molded resin products having a lengthy and slender configuration or having a special form.